U.S. patent application number 12/714139 was filed with the patent office on 2010-10-21 for impact resistant lagging, method for designing impact resistant lagging, and apparatus for testing impact resistant lagging.
This patent application is currently assigned to Jennmar Corporation. Invention is credited to Demrey Brandon, Dakota Faulkner, John Feyrer, Kevin Jinrong Ma, Robert McGinnis, John Stankus.
Application Number | 20100266349 12/714139 |
Document ID | / |
Family ID | 42981081 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100266349 |
Kind Code |
A1 |
Ma; Kevin Jinrong ; et
al. |
October 21, 2010 |
Impact Resistant Lagging, Method For Designing Impact Resistant
Lagging, and Apparatus for Testing Impact Resistant Lagging
Abstract
A steel set assembly includes a first pair of legs and a second
pair of legs with the first pair of legs being spaced from and
positioned opposite the second pair of legs. First and second beams
are provided with the first beam being secured to one leg of the
first pair of legs and one leg of the second pair of legs. The
second beam is secured to the other leg of the first pair of legs
and the other leg of the second pair of legs. A panel is secured to
the first and second beams and includes a base having a top surface
and a bottom surface, a block having a top surface and a bottom
surface, and a pad. The block is secured to the base and the pad is
positioned between the top surface of the base and the bottom
surface of the block.
Inventors: |
Ma; Kevin Jinrong;
(Cheswick, PA) ; Stankus; John; (Canonsburg,
PA) ; McGinnis; Robert; (Butler, PA) ;
Faulkner; Dakota; (Pittsburgh, PA) ; Brandon;
Demrey; (Pittsburgh, PA) ; Feyrer; John;
(Pittsburgh, PA) |
Correspondence
Address: |
THE WEBB LAW FIRM, P.C.
700 KOPPERS BUILDING, 436 SEVENTH AVENUE
PITTSBURGH
PA
15219
US
|
Assignee: |
Jennmar Corporation
Pittsburg
PA
|
Family ID: |
42981081 |
Appl. No.: |
12/714139 |
Filed: |
February 26, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61156168 |
Feb 27, 2009 |
|
|
|
Current U.S.
Class: |
405/288 ;
405/302.1; 73/12.01 |
Current CPC
Class: |
E21D 11/28 20130101;
E21D 11/18 20130101; G01N 3/30 20130101 |
Class at
Publication: |
405/288 ;
405/302.1; 73/12.01 |
International
Class: |
E21D 23/04 20060101
E21D023/04; E21D 5/00 20060101 E21D005/00; G01N 3/30 20060101
G01N003/30 |
Claims
1. A steel set assembly comprising: a first pair of legs and a
second pair of legs, the first pair of legs being spaced from and
positioned opposite the second pair of legs; first and second
beams, the first beam secured to one leg of the first pair of legs
and one leg of the second pair of legs, the second beam secured to
the other leg of the first pair of legs and the other leg of the
second pair of legs; and a panel secured to the first and second
beams, the panel comprising: a base having a top surface and a
bottom surface; a block having a top surface and a bottom surface,
the block being secured to the base; and a pad positioned between
the top surface of the base and the bottom surface of the
block.
2. The steel set assembly of claim 1, wherein the base defines a
plurality of raised portions and a receiving portion, the receiving
portion having a substantially planar surface, each raised portion
extending from the substantially planar surface, the block being
positioned in the receiving portion.
3. The steel set assembly of claim 2, further comprising an insert
positioned adjacent the bottom surface of the base, the insert
conforming to the bottom surface of the base.
4. The steel set assembly of claim 1, further comprising an insert
positioned adjacent the bottom surface of the base.
5. The steel set assembly of claim 1, wherein the block comprises a
wood crib.
6. The steel set assembly of claim 5, wherein the top surface of
the block defines a plurality of grooves.
7. The steel set assembly of claim 1, wherein the top surface of
the block defines a plurality of grooves.
8. The steel set assembly of claim 1, further comprising a
plurality of clips secured to the bottom surface of the base, the
clips securing the panel to the first and second beams.
9. The steel set assembly of claim 8, further comprising an insert
positioned between the bottom surface of the base and at least one
of the first and second beams.
10. The steel set assembly of claim 9, wherein a fastener extends
through the block, the pad, the base, and the clip.
11. The steel set assembly of claim 1, wherein the block comprises
a core and an outer shell.
12. The steel set assembly of claim 11, wherein the core comprises
a wood material and the outer shell comprises a plastic
material.
13. A panel assembly comprising: a base having a top surface and a
bottom surface; a block having a top surface and a bottom surface,
the block being secured to the base; and a pad positioned between
the top surface of the base and the bottom surface of the
block.
14. The panel assembly of claim 13, wherein the base defines a
plurality of raised portions and a receiving portion, the receiving
portion having a substantially planar surface, each raised portion
extending from the substantially planar surface, the block being
positioned in the receiving portion.
15. The panel assembly of claim 14, further comprising an insert
positioned adjacent the bottom surface of the base, the insert
conforming to the bottom surface of the base.
16. The panel assembly of claim 13, further comprising an insert
positioned adjacent the bottom surface of the base.
17. The panel assembly of claim 13, wherein the block comprises a
wood crib.
18. The panel assembly of claim 17, wherein the top surface of the
block defines a plurality of grooves.
19. The panel assembly of claim 13, wherein the top surface of the
block defines a plurality of grooves.
20. The panel assembly of claim 13, further comprising a clip
secured to the bottom surface of the base.
21. The panel assembly of claim 20, further comprising an insert
secured to the bottom surface of the base and positioned adjacent
to the clip.
22. The panel assembly of claim 21, wherein a fastener extends
through the block, the pad, the base, and the clip.
23. The panel assembly of claim 13, wherein the block comprises a
core and an outer shell.
24. The panel assembly of claim 23, wherein the core comprises a
wood material and the outer shell comprises a plastic material.
25. A testing apparatus comprising: a frame having a top end and a
bottom end; a weight block movable between the top end and the
bottom end; a guide member supported by the frame and receiving the
weight block; and a protection mechanism having a stopper and an
actuator, the stopper being operatively connected to the actuator
and movable between an extended position and a retracted position,
the stopper being configured to restrict the movement of the weight
block when in the extended position.
26. The testing apparatus of claim 25, further comprising a movable
pin having a first position and a second position, the movable pin
being received within a slot defined in the frame, the stopper
being pivotally connected to the frame via a pivot and defining a
cam surface for receiving the movable pin, wherein the actuator is
connected to the movable pin, and the stopper is in the retracted
position when the movable pin is in the first position and the
stopper is in the extended position when the movable pin is in the
second position.
27. The testing apparatus of claim 25, further comprising a base
positioned adjacent the bottom end of the frame and a load cell
positioned on the base.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/156,168, filed Feb. 27, 2009, the entire content
of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to underground mining and,
more particularly, to lagging panels for roof control at
underground openings.
[0004] 2. Description of Related Art
[0005] Certain areas of underground openings are susceptible to a
roof fall, i.e., falling rock, which presents a danger to mine
personnel. Typically, when an underground opening has experienced a
roof fall, the rock debris is removed from the area and the area of
the roof fall is bolted and backfilled to reduce the risk of
further rock fall. The process of bolting and backfilling the area
of the roof that experienced roof fall, however, is a time
consuming process that requires the mine to stop production. In
addition, backfill material is costly and backfilling the large
roof fall area can become prohibitively expensive. Accordingly,
there is a need for a simple and reliable system to protect
personnel and moving vehicles from falling rock.
[0006] Furthermore, there are currently no design guidelines and
methodologies for lagging panels available that have been
well-established to meet engineering needs in the underground
mining industry. The design of lagging panels in the mining
industry is generally based on trial-and-error and field
experiences. Therefore, a practical and reliable lagging panel
design methodology is needed which takes into account the impact
loads the panel may be subjected to from the falling rock.
SUMMARY OF THE INVENTION
[0007] In one embodiment, a steel set assembly includes a first
pair of legs and a second pair of legs with the first pair of legs
being spaced from and positioned opposite the second pair of legs.
The assembly also includes first and second beams and a panel
secured to the first and second beams. The first beam is secured to
one leg of the first pair of legs and one leg of the second pair of
legs and the second beam is secured to the other leg of the first
pair of legs and the other leg of the second pair of legs. The
panel includes a base having a top surface and a bottom surface, a
block having a top surface and a bottom surface, and a pad
positioned between the top surface of the base and the bottom
surface of the block with the block being secured to the base.
[0008] The base may define a plurality of raised portions and a
receiving portion, where the receiving portion has a substantially
planar surface and each raised portion extends from the
substantially planar surface. The block may be positioned in the
receiving portion. The panel may further include an insert
positioned adjacent the bottom surface of the base with the insert
conforming to the bottom surface of the base. The block may be a
wood crib and the top surface of the block may define a plurality
of grooves. The block may also include a core and an outer shell.
The core may be wood and the outer shell may be plastic. The
assembly may further include a plurality of clips secured to the
bottom surface of the base with the clips securing the panel to the
first and second beams. The assembly may also further include an
insert positioned between the bottom surface of the base and at
least one of the first and second beams.
[0009] In a further embodiment, a panel includes a base having a
top surface and a bottom surface, a block having a top surface and
a bottom surface, and a pad positioned between the top surface of
the base and the bottom surface of the block with the block being
secured to base.
[0010] The base may define a plurality of raised portions and a
receiving portion with each raised portion extending from the top
surface of the base and the receiving portion being defined between
the raised portions. The block may be positioned in the receiving
portion. The panel may further include an insert positioned
adjacent the bottom surface of the base with the insert conforming
to the bottom surface of the base. The block may be a wood crib and
the top surface of the block may define a plurality of grooves. The
panel may also further include a clip secured to the bottom surface
of the base and an insert secured to the bottom surface of the base
and positioned adjacent to the clip. A fastener may extend through
the block, the pad, the base, and the clip.
[0011] In another embodiment, a testing apparatus includes a frame
having a top end and a bottom end, a weight block movable between
the top end and the bottom end, a guide member supported by the
frame and receiving the weight block, and a protection mechanism
having a stopper and an actuator. The stopper is operatively
connected to the actuator and movable between an extended position
and a retracted position. The stopper is configured to restrict the
movement of the weight block when in the extended position.
[0012] The testing apparatus may further include a movable pin
having a first position and a second position. The movable pin is
received within a slot defined in the frame. The stopper may be
pivotally connected to the frame via a pivot and may define a cam
surface for receiving the movable pin. The actuator may be
connected to the movable pin. The stopper may be in the retracted
position when the movable pin is in the first position and the
stopper may be in the extended position when the movable pin is in
the second position. The testing apparatus may further include a
base positioned adjacent the bottom end of the frame and a load
cell positioned on the base.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a perspective view of a steel set assembly with
impact resistant lagging panels according to one embodiment of the
present invention;
[0014] FIG. 2 is a front view of the steel set assembly with impact
resistant lagging panels shown in FIG. 1;
[0015] FIG. 3 is a front top perspective view of the impact
resistant lagging panels shown in FIG. 1;
[0016] FIG. 4 is a front bottom perspective view of the impact
resistant lagging panels shown in FIG. 1;
[0017] FIG. 5 is a top view of the impact resistant lagging panels
shown in FIG. 1;
[0018] FIG. 6 is a side view of the impact resistant lagging panels
shown in FIG. 1;
[0019] FIG. 7 is a bottom view of the impact resistant lagging
panels shown in FIG. 1;
[0020] FIG. 8 is a front view of the impact resistant lagging
panels shown in FIG. 1;
[0021] FIG. 9 is a perspective view of a testing apparatus for a
lagging panel according to one embodiment of the present
invention;
[0022] FIG. 9A is a detail view of the protection mechanism shown
in FIG. 9;
[0023] FIG. 9B is a further detail view of the protection mechanism
shown in FIG. 9;
[0024] FIG. 10 is a front view of the testing apparatus shown in
FIG. 9;
[0025] FIG. 10A is a detail view of the load cell installed between
impact resistant lagging panel and the base of the testing
apparatus shown in FIG. 10;
[0026] FIG. 11 is a side view of a weight protection mechanism of
the testing apparatus of FIG. 9, showing the weight protection
mechanism in an extended position;
[0027] FIG. 12 is a side view of a weight protection mechanism of
the testing apparatus of FIG. 9, showing the weight protection
mechanism in a retracted position;
[0028] FIG. 13 is a front top perspective view of an impact
resistant lagging panel according to a further embodiment of the
present invention;
[0029] FIG. 14 is a front top perspective view of an impact
resistant lagging panels according to another embodiment of the
present invention;
[0030] FIG. 15 is a cross-sectional view of a block shown in FIG.
14; and
[0031] FIG. 16 is a table of the size and height of falling rock
that the lagging panel can withstand.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] For the purposes of the description hereinafter, it is to be
understood that the invention may assume various alternative
variation step sequences, except where expressly specified to the
contrary. It is also to be understood that the specific information
illustrated in the attached drawings and described in the following
specification are simply exemplary embodiments of the
invention.
[0033] Referring to FIGS. 1 and 2, one embodiment includes a three
piece long radius arch set assembly 10 having a plurality of impact
resistant lagging panels 50. The arch set assembly 10 includes
beams 14 and legs 20 formed from W8.times.31 beams, although other
types and sizes of support structure may be utilized to meet ground
control requirements. The ends of each beam 14 are secured to the
ends of respective legs 20, which are spaced from and positioned
opposite each other, via a top connection plate and gusset 30
welded to the top of the leg 20 and bolted to the beam 14. The
bottoms of the legs 20 are secured within a runner channel 35 via
bolting, although other suitable securing arrangements for the
bottoms of the legs may be provided. The runner channel 35 includes
a runner skid 37 to enable easy sliding of the runner channel 35.
Further, the arch set assembly 10 includes a tie rod and stabilizer
pipe 40 positioned adjacent to beams 14 and legs 20. In particular,
the tie rod and stabilizer pipes 40 extend perpendicularly between
adjacent beams 14 and between adjacent legs 20. Although a three
piece long radius arch set assembly 10 is disclosed, the steel set
may be a square set, two piece arch set, or any other suitable
steel set design. As discussed in more detail below, the impact
resistant lagging panels 50 are secured to the arch set assembly 10
to provide protection from falling rock for personnel and moving
vehicles positioned beneath the arch set assembly 10.
[0034] Referring to FIGS. 3-8, in one embodiment, each impact
resistant lagging panel 50 includes a base 54, a cushion pad 78, a
cushion insert 75, a clip 85, and a fastener. In particular, as
shown in FIGS. 3 and 4, for instance, each impact resistant lagging
panel includes a base 54, two impact blocks 65, two cushion pads
78, two cushion inserts 75, four clips 85, and four fasteners 90,
although other configurations and numbers of bases 54, blocks 65,
pads 78, inserts 75, clips 85 and fasteners 90 may be utilized. The
base 54 is a v-deck panel having raised portions 56a, 56b, 56c that
extend the length of the base and define a receiving space 58 for
the impact block 65, although other types of panels may be used for
the base 54. The base 54 includes a bottom surface 60 and a top
surface 62. The raised portions 56a, 56b, 56c of the base 54 extend
from the substantially planar surface of the receiving space 58 and
are generally v-shaped. Further, as shown more clearly in FIG. 8,
the base 54 includes raised portions 56a, 56c positioned along the
sides of the base 54 to allow lagging panels 50 that are positioned
adjacent to each other to interlock via the raised portions 56a,
56c. In particular, the raised portion 56a of a first panel 50 may
define a female connector to receive a male connector defined by
the raised portion 56c of a second panel 50 positioned adjacent to
the first panel 50 such that the upper surface of the raised
portion 56c engages the underside of the raised portion 56a.
[0035] The impact block 65 includes a top surface 66 and a bottom
surface 67 and is positioned in the receiving space 58 with the
cushion pad 78 positioned between the top surface 62 of the base 54
and the bottom surface 67 of the impact block 65. The top surface
66 of the impact block 65 includes a grooved surface 68 to provide
yieldability against impact, although the top surface 66 may also
be smooth or include other surface configurations. The impact block
65 may be wooden, such as a wood crib, although other suitable
materials may be used for the impact block 65. In particular, the
material of the impact block 65 should having sufficient strength
and ductility to withstand an impact from falling rock. As shown
more clearly in FIG. 4, clips 85 are provided on the bottom surface
60 of the base 54 with the fasteners 90 extending through the
impact block 65, base 54, and clips 85 to form an assembly. The
clip 85 is rotatable about the fastener 90 prior to fully
tightening the fastener 90. The cushion insert 75 is positioned
adjacent the bottom surface 60 of the base 54. As shown in FIGS. 3
and 4, the cushion insert 75 conforms to the bottom surface 60 of
the base 54, although the cushion insert 75 may have other shapes.
The fastener 90 is a bolt and nut, although any other suitable
fastening arrangement may be provided.
[0036] Referring again to FIGS. 1 and 2, the impact resistant
lagging panels 50 are positioned on the arch set assembly 10,
extending perpendicularly between adjacent beams 14. The impact
resistant lagging panels 50 are shown to only extend between
certain portions of beams 14 for the sake of clarity. In use,
however, the panels 50 will typically be provided across the full
length of the beams 14 such that there are no gaps or spaces for
falling rock to pass through. The impact resistant lagging panels
50 are secured to a flange portion 16 of the beams 14 via the clips
85. In particular, the clips 85 may be rotated to allow the base 54
to sit flush on the beams 14 and may be subsequently rotated to be
positioned beneath the flange 16 with the fasteners 90 being
tightened to ensure that the lagging panel 50 is secured to the
beam 14. When installed, the cushion insert 75 of the lagging panel
50 is positioned between the bottom surface 60 of the base 54 and
the flange 16 of the beam 14. Further, as discussed above, the
cushion pad 78 is positioned between the impact block 65 and the
base 54. Accordingly, the cushion pad 78 and the cushion insert 75
are provided to absorb impact energy from falling rock striking the
impact block 65. Further, as shown in FIG. 1, the base 54 alone may
be positioned between adjacent legs 20 of the arch set assembly
10.
[0037] Referring to FIGS. 9 and 10, one embodiment of a testing
apparatus 110 for lagging panels 50 is disclosed. The testing
apparatus 110 includes a base 115, a frame 130, guide members 145,
a pulley 155, a winch 158, a weight block 165, and dynamic load
cells 175. The base 115 includes four beams arranged in a
square-shaped structure. The frame 130 includes spaced-apart legs
132 secured to the base 115 with a top member 138 connecting the
legs 132 to each other. The frame 130 has a top end 140 and a
bottom end 142. The guide members 145 are positioned between the
spaced-apart legs 132 of the frame 130 extending from the top end
140 to the bottom end 142 of the frame 130. In particular, the
guide members 145 extend from the top member 138 towards the base
115. The guide members 145 may be a shaft constructed of pipe with
an outer diameter that is smaller than the inner diameter of pipes
that are welded to the weight block 165. The pulley 155 and winch
158 are positioned adjacent to the top member 138 of the frame 130.
The weight block 165 is positioned between the spaced-apart legs
132 of the frame 130 with the guide members 145 extending through
the weight block 165 such that the weight block 165 may be moved
along the guide members 145. The weight block 165 is movable
between the top end 140 and the bottom end 142 of the frame 130.
The weight of the weight block 165 may be changed by adding or
removing weights that are bolted to the weight block 165. A cable
(not shown) is secured to the weight block 165 and is positioned
through the pulley 155 for connection to the winch 158. A safety
protection wall 180 with a door 182 is provided that surrounds the
frame 130 and weight block 165. Further, a protection mechanism 190
is provided on the spaced-apart legs 132 of the frame 130. The
safety protection wall 180 and the weight protection mechanism 190
will be discussed in more detail below.
[0038] During use of the testing apparatus 110, a testing sample,
such as the impact resistant lagging panel 50 discussed above, is
positioned on the base 115 so that the lagging panel 50 spans
across the base 115. The span of the base 115 is designed to
simulate the span between adjacent beams 14 of the arch set
assembly 10 discussed above. The distance allows a determination of
the actual impact forces the arch set assembly 10 will receive
through the lagging panels 50. The dynamic load cells 175 are
positioned between the lagging panel 50 and the base 115 of the
testing apparatus 110. In particular, as shown more clearly in FIG.
10, the dynamic load cells 175 are positioned beneath each corner
of the lagging panel 50 on the base 115. Prior to placing the
lagging panel 50 for testing, the weight block 165 is raised along
the guide members 145 using the winch 158. The weight block 165 is
dropped by releasing the electronically-controlled winch 158 such
that the weight block 165 free falls and impacts the lagging panel
50 positioned on the base 115. The readings from the dynamic load
cells 175 may be recorded using a data acquisition system (not
shown). The total impact force may be determined by taking the
summation of the peak forces from the dynamic load cells 175. The
weight block 165 may then be raised again so that the lagging panel
50 can be replaced for an additional test. The testing apparatus
110 consistently tests variations in the design of the lagging
panels 50. In particular, the testing apparatus 110 consistently
records the amount of instantaneous force that the lagging panel 50
is subjected to during a dynamic impact process. Through repeated
testing of variations in design, the relative impact strength of
each lagging panel 50 design can be determined.
[0039] Referring again to FIGS. 9 and 10, the testing apparatus 110
is surrounded by the safety protection wall 180 to shield personnel
from flying debris caused by the impact of the weight block 165.
Further, the protection wall 180 may be provided with two front and
back split doors 182 that have sensors (not shown) to determine if
they are closed and locked. In order for the weight block 165 to be
raised, a control panel (not shown) will sense that the doors 182
are closed and locked. The doors 182 will be locked until the
weight block 165 has reached the protection mechanism 190 or until
the weight block 165 is in a lowered position. The protection wall
180 and the doors 182 may be constructed of plastic, such as
polycarbonate, although other suitable materials may be used.
[0040] Referring to FIGS. 9-12, the protection mechanism 190, which
is disposed between the spaced-apart legs 132 of the frame 130,
includes a stopper 192 with a cam surface 194, a movable pin 196, a
pivot 198, and an actuator 199. A protection mechanism 190 may be
provided on each of the spaced-apart legs 132 of the frame 130. The
pivot 198 is disposed through a bottom portion of the stopper 192
and secured to the leg 132 of the frame 130 such that the stopper
192 is pivotable about the pivot 198. The movable pin 196 is
disposed through a slot 134 defined in the leg 132 of the frame
130. The cam surface 194 of the stopper 192 is configured to
receive the movable pin 196. The movable pin 196 has a first
position, shown in FIG. 12, and a second position, shown in FIG.
11. The actuator 199, which is shown more clearly in FIG. 9B, is
operatively connected to the movable pin 196 to move the pin 196
within the slot 134 of the leg 132 between the first and second
position. The stopper 192 has an extended position, shown in FIG.
11, and a retracted position, shown in FIG. 12. In the extended
position, the actuator 199 moves the movable pin 196 to the second
position toward the bottom of the slot 134 in the leg 132, which,
due to the arrangement of the cam surface 194 of the stopper 192,
extends the stopper 192 from the leg 132. In the retracted
position, the actuator 199 moves the movable pin 196 to the first
position toward the top of the slot 134 in the leg 132, which, due
to the arrangement of the cam surface 194 of the stopper 192,
retracts the stopper 192 to a position within the leg 132 of the
frame 130. In other words, when the movable pin 196 is moved from
the first position to the second position, the movable pin 196
engages the cam surface 194 of the stopper 192 thereby pivoting the
stopper 192 about the pivot 198. When the weight block 165 is in a
raised position, the stopper 192 of the protection mechanism 190
may be placed in the extended position such that the weight block
165 rests on the stopper 192. In case of a power failure and
release of the winch 158, the weight block 165 will be supported by
the weight protection mechanism 190 thereby preventing possible
injury to personnel positioned beneath the weight block 165. When
the weight block 165 is raised and hits the stopper 192, the cam
surface 194 of the stopper 192 allows the stopper to rotate out of
the way then spring back once the weight block 165 slides by. The
weight protection mechanism 190 will only be disengaged when the
operator is ready to drop the weight block 165.
[0041] Referring to FIG. 13, a further embodiment of an impact
resistant lagging panel 50' is disclosed. The impact resistant
lagging panel 50' is substantially similar to the lagging panel 50
described above and may be used similarly in arch set assembly 10,
except each impact block 65 is provided as a top block 95 and a
bottom block 96 with the cushion pad 78 positioned between the top
and bottom blocks 95, 96. The cushion pad 78 provides further
impact absorption for the lagging panel 50'.
[0042] Referring to FIGS. 14 and 15, another embodiment of an
impact resistant lagging panel 50'' is disclosed. The impact
resistant lagging panel 50'' is substantially similar to the
lagging panel 50 described above and may be used similarly in arch
set assembly 10. Rather than being provided with the impact block
65 described above, however, the panel 50'' includes an impact
block 98 having a core 101 with an outer shell 103. The core 101
may be formed from wood or steel and the outer shell may be formed
from a composite plastic. In a particular embodiment, the core 101
is formed from treated hard wood and the outer shell 103 is formed
from soft to medium soft recycled rubber or recycled plastic. The
outer shell 103 may be substantially impermeable to moisture. In
certain embodiments, the outer shell 103 is formed from a composite
plastic material commercially available from IntegriCo Composities
located at 4310 Lucius McCelvey Drive, Temple, Tex. 76504. The ends
of the block 98 are shown having a portion of the core 101 being
exposed, but the outer shell 103 may be provided such that the
shell 103 completely encompasses the core 101. It has been found
that the block 98 having plastic shell 103 exhibits enhanced
durability (particularly moisture resistance), impact resistance,
and strength as compared to blocks not having a plastic shell. In
one non-limiting embodiment, the core 101 is sized about 3.5 inches
by 3.5 inches and the shell 103 is about 1 to 2 inches thick.
Although the impact resistant lagging panel 50'' does not include
the pad 78 of the panel 50 described above, the panel 50'' may also
include the pad 78. In addition, core 101 within block 98 may be
provided with a grooved surface (not shown) as in block 65. The
outer surface of the outer shell 103 may also be provided with a
grooved surface (not shown) as in block 65.
[0043] In a further embodiment, a method of designing an impact
resistant lagging panel is disclosed. The method includes: a)
estimating the size of falling rock and roof fall height; b)
applying impulse-momentum theory based on values obtained in step
a) to obtain an impact load value; and c) designing a lagging panel
based on the impact load value. The method may also include the
step of fabricating a lagging panel based on the design obtained in
step c).
[0044] The size of the falling rock and the roof fall height may be
estimated based upon an evaluation of rock strata and roof
condition. The condition of the rock strata may be determined based
on core samples previously taken as well as information known to
mine operators through experience of operating in a particular
area. For instance, if the immediate roof is known to be thinly
laminated, the rocks from a secondary roof fall will generally be
small in size. The size of falling rock and roof fall height may
also be estimated based on previous roof falls in the area.
[0045] Once the size and height of the falling rock is estimated,
the impulse-momentum theory may be applied. The impulse-momentum
theory is described by the following equations:
P.DELTA.t=M(V.sub.f-V.sub.i) (Equation 1)
M=(w).times.(t).times.(s).times.(.gamma.) (Equation 2)
V.sub.i= 2gH (Equation 3)
[0046] P is the impact load;
[0047] .DELTA.t is the duration of impact;
[0048] M is the mass;
[0049] w is the width of the falling rock;
[0050] t is the thickness of the falling rock;
[0051] s is the unit length of the rock layer (s=1);
[0052] .gamma. is the average density of fractured rock (assuming
120 lb/ft.sup.3 or other appropriate value);
[0053] V.sub.i is the velocity of the falling rock before
impact;
[0054] H is the falling height;
[0055] g is the gravitational acceleration;
[0056] V.sub.f is the velocity of falling rock after impact
(assuming 0).
[0057] The size of the falling rock, i.e., the width (w) and
thickness (t), is obtained from the estimation in the previous
step. The falling height (H) is also obtained from the estimation
in the previous step. Thus, the mass (M) and the velocity of the
falling rock before impact (V.sub.i) can be calculated using
Equations 2 and 3. Although the average density of the fractured
rock (.gamma.) was assumed to be 120 lb/ft.sup.3, other appropriate
values may be used. The duration of the impact (.DELTA.t) is
dependent on the properties of the lagging panel 50 being impacted.
For instance, the ductility of the impact block and the amount and
type of cushioning used in the lagging panel 50 will affect the
duration of the impact (.DELTA.t). The duration of the impact
(.DELTA.t) for a particular lagging panel arrangement may be
determined through laboratory testing, which will be discussed
below in more detail. Because the rest of the values are now known,
the impact load (P) may then be determined using Equation 1. Based
upon the impact load (P) value, a lagging panel 50 may be designed
to withstand the impact from falling rock.
[0058] The method may further include the step of performing finite
element computer modeling to determine the dynamic impact support
capacity of a particular lagging panel. The impact resistant
lagging panel 50, which was discussed above, was modeled to
determine the dynamic impact support capacity assuming the lagging
panel 50 is supported over a 4 foot span by W8.times.31 beams on
both ends. The vertical deformation and safety factor distribution
of the impact resistant lagging panel 50 at the given impact load
(P) are determined from the computer model. More specifically, with
68 kips of impact load (P) at the mid-span, the supported beam
develops less than 0.16'' deflection at the mid-span, and material
yielding initiates at the outmost fiber at the bottom of the V-deck
panel and at the top of the wood cribs. Since the lagging panel 50
deflects within the serviceability range (typically 1/360 span) and
the yielding zone does not propagate thru the impact blocks, it can
be concluded that the lagging panel 50 has adequate strength to
sustain 68 kips of dynamic impact load (P). If the design of the
lagging panel 50 is determined to be insufficient from the computer
modeling, the design of the panel 50 may be modified by altering
the size of the components, selecting alternative materials, or
making other suitable changes to the design to ensure the panel can
sustain the estimated impact loads. The design process may be
repeated to select a design that has a suitable dynamic impact
support capacity. Accordingly, finite element computer modeling may
be used to design a lagging panel 50 to withstand the impact load
(P) determined using Equation 1.
[0059] The peak impact load (P) and the duration of the impact may
be determined by conducting a test using the testing apparatus 110
shown in FIGS. 9 and 10 and discussed in more detail above. To
simulate the actual loading condition, the weight block 165 falls
down freely at a height of approximately 7' above the lagging panel
50. The weight block 165 may weigh 500 to 1000 lbs. The four
dynamic load cells 175 are positioned underneath the lagging panel
50 and a computerized data acquisition system identifies
instantaneous peak impact load (P) and duration of impact. The
tests may be conducted using different lagging panel 50
configurations. Through the testing, the duration of impact of the
impact resistant lagging panel was determined to be approximately
0.25 second, which was an increase in the duration of time of
impact over other lagging panel configurations without the impact
block 65 and cushions 75, 78. Thus, the impact resistant capacity
of the impact resistant lagging panel 50 was dramatically
increased.
[0060] Based on the laboratory testing and finite element analysis
of the lagging panel 50, a maximum impact load the panel can
sustain without failure is determined. Referring to FIG. 16, a
table can be compiled showing various sizes of falling rock for
different falling heights, which represent the maximum values
(height and size of falling rock) that the lagging panel 50 can
sustain. The values in the table are provided assuming the lagging
panel 50 can sustain 68 kips of impact load (P) within 0.25 second
duration. The table may be used to determine if the lagging system
will be destroyed by falling rock by making a visual estimate of
possible size and height of the falling rock in the field. For
example, the impact resistant lagging panel can sustain an
instantaneous load generated by a maximum 2' thick, 2.5.degree.
wide rock layer falling at a 20' height from the top of the arch
set.
[0061] The above invention has been described with reference to the
preferred embodiments. Obvious modifications, combinations and
alterations will occur to others upon reading the preceding
detailed description. Accordingly, the foregoing description is
intended to be illustrative rather than restrictive.
* * * * *